ISSN:
0362-2525
Keywords:
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
Electron microscopy was used to follow the transformation of the endostyle to a thyroid gland in the anadromous sea lamprey, Petromyzon marinus L., throughout metamorphosis (stages 1-7). Transformation of the larval (ammocoete) endostyle begins at the first signs of external change (stages 1-2), and the adult form of the gland is reached by stage 5. Only slight modifications of the gland accompany further development to the end of metamorphosis.Development of the thyroid gland involves degeneration, proliferation, and reorganization of the cells in the endostyle, and changes in their fine structure. Ultrastructural changes during early stages are most obvious in the type 1 cells that make up the shrinking glandular tracts, and involves the accumulation of cytoplasmic microfilaments and a variety of cytoplasmic inclusions. The glandular tracts and their cells gradually disappear through autolysis and, apparently, through phagocytosis by neighboring epithelial cells and macrophages. Although the fine structure of the type 2, 3, 4, and 5 cells is not altered in the early stages, by stage 3, many of these cells become either vacuolated, undergo autolysis, or are extruded. Phagocytosis of some of each of these cell types likely occurs.Thyroid follicles are first observed during stage 4. Some of their lumina seem to arise from the accumulation of material in intercellular spaces and from vacuoles among cell clusters. Other lumina may represent a portion of the original lumen of the endostyle. Many follicles appear to be comprised of cells with cytological characteristics similar to those of larval cell types 3 and 2c. Some of the other larval cell types, such as type 5, may also be involved. In young adult lampreys follicles are composed of cuboidal to columnar cells that lack the dilated cisternae of rough endoplasmic reticulum seen in follicular cells of higher vertebrates. Dense collagenous connective tissue surrounding the follicles contains relatively few blood vessels.The transformation process described may have some relevance to our understanding of the development and evolution of the vertebrate thyroid gland.
Additional Material:
30 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jmor.1051660209
